Stormwater runoff is characterized by the United States Environmental Protection Agency as one of the greatest remaining sources of water pollution in America. Thus, efforts to implement stormwater quality improvement regulations are accelerating across the United States, compelling municipalities and land developers to maximize the usefulness and effectiveness of stormwater infrastructure.
In urban, suburban, and commercial settings polluted stormwater is often collected in a catch basin. In its simplest form, a catch basin functions to intercept surface water flows in order to prevent the accumulation of stormwater in an area where flooding could impede traffic or pedestrians, cause property damage, or otherwise present a nuisance. Stormwater, also referred to as wastewater, collects in the catch basin, and flows through a network of pipes, sewers, and additional catch basins to an outlet point such as a lake, stream, river, ocean, unpopulated area, or similar location where the wastewater is dispersed without the threat of flood or property damage. However, catch basins are also often the entry point of pollutants from diffuse sources found in stormwater runoff. For example stormwater runoff may contain pollutants such as hydrocarbons (also referred to as “oil”), bacteria, sediment, trash, organic material such as leaves, grass clippings, sediment, detergents, coolants, grease, fertilizer, paint, and feces. As a result, wastewater is often discharged untreated, directly into lakes, streams, and oceans.
As discussed in U.S. Pat. No. 6,126,817 to Duran et al., which is hereby incorporated by reference, many types of equipment and processes have been suggested in the past for reducing the level of pollutants in wastewater. Many of these systems are based on the principle of differential specific gravity separation. The liquid mixture, which usually is wastewater, flows slowly through an elongated path in a liquid-retaining structure, such as, for example, a catch basin. The matter to be collected is usually oil and floatable debris, both of which accumulate on the surface of the wastewater because they have a specific gravity lower than that of water. Alternatively, as the wastewater flows through the catch basin solids carried by the wastewater accumulate on the bottom of the basin. These solids sink to the bottom of the catch basin because they have a specific gravity greater than water.
U.S. Pat. No. 6,126,817 discloses a novel outlet hood (or “hood”) for use in a catch basin to reduce the flow of oil and other pollutants into an outlet pipe in the catch basin. The hood is useful for capturing trash and floatables, and modest levels of free oils, and sediment. The hood is sealably mounted to the wall of a catch basin over the outlet pipe in the wall of the catch basin. The hood is installed on the wall of the catch basin such that the bottom of the hood is below the lowest level of the outlet pipe. As wastewater collects in the catch basin heavier pollutants sink and collect on the bottom of the catch basin. Other pollutants having a specific gravity less than water, such as debris, floatables, and oil float on the surface of the wastewater.
The bottom of the hood prevents pollutants with a specific gravity lower than water from entering the outlet pipe since the bottom of the hood extends below the water line of the wastewater. As the wastewater level rises in the catch basin, water flows underneath the bottom of the hood, which is well below the surface of the water, and into the outlet pipe. Pollutants with a specific gravity lower than water, however, remain on the surface of the wastewater. The wall of the hood acts as a barrier and prevents the oil and other floatables from flowing into the outlet pipe. Periodically, the catch basin is cleaned to remove oil and other floatables that have accumulated therein, as well as sediment that has accumulated in the bottom of the catch basin. In this way the hood provides an inexpensive means of reducing the level of pollution in wastewater.
A known problem with such hood systems is that, while they retain oil and other floatables for later collection, there is no means for absorbing pollutants, for example oil, bacteria, and chemicals, that collect on the surface of the wastewater between scheduled maintenance collections. Many times the scheduled maintenance collections occur infrequently, for example once per year, or every other year. As a result pollutants collect on the surface of the wastewater in the catch basin. Overtime some of the collected pollutants can be drawn below the surface of the wastewater and below the bottom level of the hood, and into the outlet pipe as a result of pressure gradients that are generated by water exiting and entering the catch basin. This problem is compounded during high wastewater flow events when the volume of wastewater passing through the catch basin greatly increases. The high flow rate creates turbulent conditions in the wastewater flowing through the catch basin, thereby increasing the opportunity for pollutants to flow under the bottom of the hood and into the outlet.
One known solution to this problem is to place a pollutant absorbent boom into the catch basin so that it floats on top of the wastewater and absorbs pollutants, such as oil, that are retained in the catch basin. The pollutant absorbent boom floats freely on the top surface of the wastewater, so that it absorbs oil and other pollutants on the top surface of the wastewater. Periodically, the pollutant absorbent boom becomes saturated with oil and other pollutants and is replaced with a new or cleaned absorbent boom. Replacing the boom is relatively easy because it floats freely on the wastewater in the catch basin, thus an absorbent boom can be replaced without the need for maintenance personnel to enter the catch basin. This is preferred because any maintenance procedure that requires entry into the catch basin increases the maintenance time and therefore cost.
One example of an absorbent boom used to reduce pollutants is the skirted boom sold by Eco-Tec, Inc. under the trade name the Hula Bug™. The skirted boom comprises an absorbent boom that floats on the surface of the water and a skirt that hangs down therefrom. The boom may be formed into a circle by connecting the two ends of the boom and then placed into a catch basin. The skirted boom floats freely across the surface of the wastewater and collects oil and oil-borne contaminants. The skirt, which may comprise a series of tendrils, hangs below the boom in the wastewater and provides additional absorbent surface area while the separation between tendrils allows wastewater to pass.
A disadvantage of free floating absorbent pads or booms is that they must be periodically replaced to maintain a consistent level of pollutant reduction. Once a boom becomes saturated with oil and other pollutants, it cannot absorb additional pollutants that continue to flow through the catch basin and into the outlet pipe.
Another disadvantage of known skirted booms is that they float freely on the surface of the wastewater.
Another disadvantage of known skirted booms is that that they are less effective at retaining pollutants during high flow events such as a rainstorm. During relatively low flow conditions, the skirted boom floats on the surface of the wastewater and collects pollutants. As the rate of flow increases the absorbent boom has less time to absorb an increasing amount of pollutants flowing through the catch basin.
Another disadvantage of known skirted booms is that they do not prevent turbulent water flows from drawing floatables, trash and other debris into the outlet pipe of the catch basin.
What is desired therefore, is an apparatus for reducing the flow of pollutants such as hydrocarbons, bacteria, and other floatables into the outlet of a catch basin. Another desire is an apparatus and a method for using the same wherein the apparatus combines a hood and a skirted boom in a configuration that more efficiently and more consistently reduces the flow of pollutants into the outlet of a catch basin. Another desire is a method of installing and removing such an apparatus without the need for personnel to enter the catch basin. What is further desired is a system and method for reducing pollutants floating on the surface of the wastewater from being drawn under the bottom of an installed hood by turbulent wastewater.